Heated air won't be a problem, because I don't blow it into the organ. I suck it away from the organ.
As I wrote, I'd like to run the motor on slowest possible speed, because that would probably the quietest mode, too. But I might end up in building a box with a sliding plate over a hole. A pressure gauge inside the organ and a servo doing the sliding. The wind chest inside the organ usually has a valve, which regulates the pressure. But it keeps noise when it opens. So using the vacuum with too high effect would cause a constant noise.